Color conversion particle

ABSTRACT

A color conversion particle includes a core; and a shell that contains the core and absorbs excitation light, and emits light at the core or at an interface between the core and the shell upon receiving the irradiated excitation light. The core is composed of a chalcogenide perovskite, and the core and the shell have band alignment that induces a Stokes shift.

TECHNICAL FIELD

The present invention relates to a color conversion particle.

BACKGROUND ART

Conventionally, in lighting, display devices, solar cells, and the like,color conversion using wavelength conversion (downconversion) ofconverting excitation light incident on an object from the outside intolight having a longer wavelength and emitting the light has been widelyutilized. In this type of color conversion, for example, a phosphor towhich an activator is added may be used. However, conventional phosphorshave limitations in controllability of an emission wavelength, anemission peak width, and the number of peaks (color purity), and forexample, there are many problems to be improved in applicationsrequiring high color purity at a specific wavelength such as a displaydevice.

On the other hand, in recent years, core-shell quantum dots to which thequantum effect is applied have attracted attention as solutions to theabove problems, and core-shell quantum dots are being applied in variousfields. A core-shell quantum dot is a minute semiconductor particlehaving a diameter of several nanometers, and has a structure in which acore functioning as a light emission unit is covered from the outside bya shell functioning as a carrier confinement layer or a light absorptionunit.

In this type of core-shell quantum dot, the substance of the core isselected from, for example, Cd(S, Se), InP, and APbX₃ (A=Cs, MA; X═Cl,Br, I). The substance of the shell is, for example, Zn(S, Se) or A′₂PbX₄(A′=OA) Here, MA is methyl ammonium and OA is octyl ammonium. Inaddition, as a material of the quantum dot, a halide perovskiterepresented by CsPbBr, a chalcogenide perovskite constituted by achemical formula ABX₃ (A=Ca, Sr, Ba; B═Ti, Zr, Hf; X═S, Se, Te), and thelike are also known.

CdSe, which is one of the materials of the core-shell quantum dots,contains Cd restricted by RoHS and has toxicity. Therefore, InP has beendeveloped as an alternative material to Cd(S, Se), but InP has problemsin terms of material durability and light emission efficiency inaddition to containing the rare metal In. In addition, a halideperovskite has high absorbance and light emission efficiency, but thematerial durability is not sufficient.

On the other hand, the chalcogenide perovskite has a large lightabsorption coefficient and excellent durability. In addition, since thechalcogenide perovskite has a steep absorption end profile, excellentlight emission performance can also be expected. For example, PatentLiterature 1 discloses a quantum dot using a chalcogenide perovskite.

CITATION LIST Patent Literature

-   Patent Literature 1: US 2019/0225883 A

SUMMARY OF INVENTION Technical Problem

However, the quantum dot of the chalcogenide perovskite is excellent inlight absorbability, but also has a large loss due to reabsorption oflight emission. When the particle size is reduced in order to suppresssuch a reabsorption loss, the absorbance decreases. That is, there was atrade-off relationship between the absorbance and the reabsorption loss.

The present invention has been made in view of the above circumstances,and provides a color conversion particle that achieves high absorbanceand high light emission efficiency while suppressing light emissionreabsorption loss.

Solution to Problem

According to an aspect of the present invention, there is provided acolor conversion particle including: a core; and a shell that containsthe core and absorbs excitation light, and emits light at the core or atthe interface between the core and the shell upon receiving theirradiated excitation light. The core is composed of a chalcogenideperovskite, and the core and the shell have band alignment that inducesa Stokes shift.

Advantageous Effects of Invention

According to the color conversion particle of the present invention, itis possible to achieve high absorbance and high light emissionefficiency while suppressing light emission reabsorption loss.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic diagram showing a configuration example of a colorconversion particle of the present embodiment.

FIG. 2 is a graph showing an example of a relationship betweenexcitation energy and a particle radius.

FIG. 3 is a graph showing an example of a relationship betweenexcitation energy and a particle radius based on physical propertyvalues of BaZrS₃.

FIG. 4 is a diagram showing an example of band alignment of a core and ashell.

FIG. 5 is a diagram showing an example of band alignment of the core andthe shell.

FIG. 6 is a diagram showing an example of band alignment of the core andthe shell.

FIG. 7 is a diagram showing a modification example of the colorconversion particle of the present embodiment.

FIG. 8 is a diagram showing a modification example of the colorconversion particle of the present embodiment.

FIG. 9 is a diagram showing band alignment of the core and the shell inan example.

FIG. 10 is a diagram showing a result of simulation of the example.

FIG. 11 is a diagram showing respective profiles of light absorptioncoefficients of BaZrS₃ and SrZrS₃ and a PL emission spectrum of BaZrS₃.

FIG. 12 is a diagram showing a correspondence between a combination ofmaterials of a core and a shell, and a type of band alignment andexpression of a Stokes shift in the example and comparative example.

DESCRIPTION OF EMBODIMENTS

Hereinafter, embodiments will be described with reference to thedrawings as appropriate.

In the embodiment, for ease of description, structures or elements otherthan the main parts of the present invention will be described in asimplified manner or omitted. In the drawings, the same elements aredenoted by the same reference numerals. In the drawings, shapes,dimensions, and the like of each element are schematically shown, and donot indicate actual shapes, dimensions, and the like.

<Structure of Color Conversion Particle>

FIG. 1(a) is a schematic diagram showing a configuration example of acolor conversion particle of the present embodiment.

A color conversion particle 10 has a particle shape with a nanometerscale as a whole, and absorbs incident excitation light and reemits(emits) light with different energy (wavelength) to perform colorconversion.

The color conversion particle 10 includes a core 11 as a light emissionunit and a shell 12 as a light absorption unit. The shell 12 containsone or more cores 11 therein. Then, a part or the whole of each core 11is covered with the shell 12 from the outside to form the colorconversion particle 10.

In the color conversion particle 10, the core 11 and the shell 12 areprovided separately, and a chalcogenide perovskite is adopted as amaterial of the core 11. As a result, the high absorbance and the highlight emission performance of the core 11 with respect to the excitationlight are realized, and the durability of the color conversion particle10 is also improved. This point will be described later.

In addition, in the core 11 and the shell 12, the band alignment ofenergy E_(c) at the lower end of the conduction band and energy E_(v) atthe upper end of the valence band induces a Stokes shift. Band alignmentof the core 11 and the shell 12 will be described later.

Furthermore, by adjusting the band gap between the core 11 and the shell12, it is possible to impart a characteristic of transmitting lightemitted from the core 11 to the shell 12. As a result, in the colorconversion particle 10, the light generated in the core 11 can besuppressed from being reabsorbed by the shell 12.

<Core 11>

The core 11 is a light emitting particle made of a semiconductormaterial that generates fluorescence of a target emission wavelength byexcitation light. The core 11 as a light emitting particle causeselectron-level transition having energy corresponding to a targetemission wavelength.

(Material of Core)

The core 11 is composed of a chalcogenide perovskite.

The chalcogenide perovskite is a semiconductor composed of a perovskitecrystal structure group containing chalcogen elements (S, Se, and Te) atthe X site, and includes a semiconductor in which a part of the X siteis substituted with oxygen (O).

The perovskite described above represents a substance group having acubic crystal structure having a BX₆ octahedron as a skeleton, which isrepresented by the chemical formula ABX₃, and can take a tetragonal ororthorhombic crystal structure due to lattice distortion. In addition, aplurality of stable crystal structures are shown computationally in asimilar ABX₃ composition. These crystal structures include structuresclose to perovskites as well as significantly different structures.Further, as the derivative structure, there are a Ruddlesden-Popper typeor Dion-Jacobson type layered perovskite based on a perovskitestructure, a double perovskite crystal structure in which differentelements are alternately arranged at the B site, and the like.

In the present specification, the above-described crystal structure iscollectively referred to as a “perovskite crystal structure group.”

The perovskite crystal structure group specifically includes a substancehaving the following crystal structure.

Cubic perovskite, tetragonal perovskite, GdFeO₃ type orthorhombic, YScS₃type orthorhombic, NH₄CdCl₃ type orthorhombic, BaNiO₃ type hexagonal,FePS₃ type monoclinic, PbPS₃ type monoclinic, CeTmS₃ type monoclinic,Ruddlesden-Popper type layered perovskite, Dion-Jacobson type layeredperovskite, and double perovskite

In the perovskite crystal structure group, the crystal structure and theelectronic structure change depending on the composition and synthesisconditions, and the photoelectronic properties and the chemicalcharacteristics change. Therefore, the composition and conditions areselected to obtain a crystal structure suitable for the purpose.

For example, a substance having a cubic perovskite, a tetragonalperovskite, a GdFeO₃ type orthorhombic perovskite, a Ruddlesden-Poppertype layered perovskite, or a double perovskite structure has excellentphotoelectronic properties and chemical characteristics. In addition,the Dion-Jacobson type layered perovskite structure can further improvechemical stability.

In particular, a substance having a crystal structure of a GdFeO₃ typeorthorhombic perovskite represented by ABX₃ (A=Group 2, B=Group 4) isknown to have excellent photoelectronic properties including a highlight absorption coefficient.

In addition, the chemical formula of the chalcogenide perovskite can berepresented by ABX₃, A′₂A_(n−1)B_(n)X_(3n+1), A″A′″B″₂X₇, A″A₂B″₃X₁₀,and A₂BB′X₆.

In the above chemical formulae, X represents chalcogen elements (S, Se,and Te). A and A′ represent Group 2 elements (Ca, Sr, and Ba), A″represents Group 1 elements (Li, Na, K, Rb, and Cs), and A′″ representsGroup 3 elements (rare earth elements) and Bi. B and B′ represent Group4 elements (Ti, Zr, and Hf), and B″ represents Group 5 elements (V, Nb,and Ta). In addition, n is a positive integer. Further, A and A′ may bethe same element, as may B and B′. In addition, A, A′, A″, A′″, B, B′,B″, and X include those obtained by mixing elements of the respectivegroups at any ratio.

Examples of the chalcogenide perovskite represented by the chemicalformula ABX₃ include the following substances. In the following example,X is selected from (S, Se) which are superior materials among chalcogenelements, A is selected from (Sr, Ba) which are superior materials amongGroup 2 elements, and B is selected from (Zr, Hf) which are superiormaterials among Group 4 elements.

SrZrS₃, SrZrSe₃, SrHfS₃, SrHfSe₃, BaZrS₃, BaZrSe₃, BaHfS₃, and BaHfSe₃

In addition examples of the chalcogenide perovskite represented by thechemical formula A′₂A_(n+1)B_(n)X_(3n+1) include the followingsubstances. X is selected from (S, Se) which are superior materialsamong chalcogen elements, A and A′ are selected from (Sr, Ba) which aresuperior materials among Group 2 elements, and B is selected from (Zr,Hf) which are superior materials among Group 4 elements.

Sr₂Ba_(n−1)Zr_(n)S_(3n+1), Sr₂Ba_(n−1)Zr_(n)Se_(3n+1),Sr_(n+1)Zr_(n)S_(3n+1), Sr_(n+1)Zr_(n)Se_(3n+1),Ba₂Sr_(n−1)Zr_(n)S_(3n+1), Ba₂Sr_(n−1)Zr_(n)Se_(3n+1),Ba_(n+1)Zr_(n)S_(3n+1), Ba_(n+1)Zr_(n)Se_(3n+1),Sr₂Ba_(n−1)Hf_(n)S_(3n+1), Sr₂Ba_(n−1)Hf_(n)Se_(3n+1),Sr_(n+1)Hf_(n)S_(3n+1), Sr_(n+1)Hf_(n)Se_(3n+1),Ba₂Sr_(n−1)Hf_(n)S_(3n+1), Ba₂Sr_(n−1)Hf_(n)Se_(3n+1),Ba_(n+1)Hf_(n)S_(3n+1), and Ba_(n+1)Hf_(n)Se_(3n+1)

The chalcogenide perovskite can also be expressed as(Sr_(x)Ba_(1−x))(Zr_(y)Hf_(1−y))(S_(z)Se_(1−z))₃ or(Sr_(x)Ba_(1−x))₂(Sr_(x)Ba_(1−x))_(n−1)(Zr_(y)Hf_(1−y))_(n)(S_(z)Se_(1−z))_(3n+1)(where each of x, x′, y, and z is a value from 0 to 1).

Note that the superior materials in X, A, A′, and B described above arematerials having a band gap suitable for applications that emit visiblelight, such as a light emitting device, a display device, and a lightingdevice, when applied to the color conversion particle 10.

Here, examples of the material of the core that emits red light includeBaZrS₃. Examples of the material of the core that emits red lightinclude SrHfS₃. Examples of the material of the core that emits bluelight include BaZr(O,S)₃.

In the chalcogenide perovskite, a carrier concentration or a crystalstructure can be controlled or other physical and chemical propertiescan be adjusted by partial substitution of a constituent element with anelement of the same or a different group. For example, the Group 1elements can be substituted with elements of Groups 1 and 2, the Group 2elements can be substituted with elements of Groups 1, 2, and 3, theGroup 3 elements can be substituted with elements of Groups 2, 3, and 4,the Group 4 elements can be substituted with elements of Groups 3, 4,and 5, and the Group 16 elements can be substituted with elements ofGroups 15, 16, and 17.

The chalcogenide perovskite has the following features.

The chalcogenide perovskite has a large light absorption coefficient andexcellent light emission performance (light emission efficiency andhalf-value width). In addition, the profile of the light absorptioncoefficient of the chalcogenide perovskite sharply rises at the bandend. Therefore, the chalcogenide perovskite has a characteristic thatthe absorbance in the vicinity of the band gap end is high.

Therefore, the chalcogenide perovskite core 11 has high absorbance andcan efficiently absorb excitation light.

In addition, the chalcogenide perovskite has high chemical stability,and is excellent in durability against external environments and stimulisuch as the atmosphere, moisture, heat, and light. Therefore, thechalcogenide perovskite core 11 has high durability, and can suppressdeterioration of the core 11.

Furthermore, the chalcogenide perovskite has high safety because toxicelements are not contained, and is also advantageous in that rawmaterial cost is low because rare metals are not contained.

(Core Size)

Next, the core size will be described after the quantum dot is describedas a premise.

When a semiconductor is used for light emitting particles, basically,fluorescence, which is generated when interband recombination betweenelectrons excited in a conduction band and holes in a valence bandoccurs, is used for light emission. Therefore, the emission wavelengthin the light emitting particle corresponds to the band gap energyE_(g,bulk) of the bulk.

When the particle size of the light emitting particles is reduced andthe quantum size effect due to electron confinement is remarkablyexhibited, the energy level of the electron becomes discrete. In thiscase, the energy (band gap) E_(ex) in the lowest excited state isgreater than E_(g,bulk) and depends on the particle size. That is, whenthe particle size of the light emitting particles decreases, theemission wavelength shifts to a shorter wavelength side than the bulkstate, and the emission wavelength changes depending on the particlesize. By utilizing this property, the emission wavelength of the lightemitting particles can be controlled.

Specifically, E_(ex) of the light emitting particle having a radius r isgiven by the following formula. Note that μ represents an excitonequivalent mass, E_(b,ex) represents exciton binding energy, and r_(B)represents an exciton Bohr radius.

$\begin{matrix}{E_{ex} = {E_{g,{bulk}} + {\frac{\hslash^{2}}{2\mu}( \frac{\pi}{r} )^{2}} - {E_{b,{ex}}\lbrack {{3.572( \frac{r_{B}}{r} )} + {{0.2}48}} \rbrack}}} & \lbrack {{Math}.1} \rbrack\end{matrix}$

μ, E_(b,ex), and r_(B) are each given by the following formula with s asthe dielectric constant of the light emitting particle. Note that m*_(e)is an effective mass of electrons, and m*_(h) is an effective mass ofholes.

$\begin{matrix}{\mu = \frac{m_{e}^{*}m_{h}^{*}}{m_{e}^{*} + m_{h}^{*}}} & \lbrack {{Math}.2} \rbrack\end{matrix}$ $E_{b,{ex}} = \frac{\hslash^{2}}{2\mu r_{B}^{2}}$$r_{B} = \frac{4\pi{\varepsilon\hslash}^{2}}{\mu e^{2}}$

FIG. 2 is a graph showing dependency of E_(ex) on r when μ=0.1 and ε=10.The vertical axis of FIG. 2 represents E_(ex)/E_(g,bulk), and thehorizontal axis of FIG. 2 represents r/r_(B). As the radius r of thelight emitting particle decreases and approaches r_(B), the value ofE_(ex) gradually increases from E_(g,bulk). When r is equal to or lessthan r_(B), the value of E_(ex) remarkably increases (quantum sizeeffect).

A light emitting particle having a particle size in a range in which theemission wavelength depends on the particle size based on r_(B) definedby the above formula by utilizing the characteristics of the quantumsize effect is referred to as a “quantum dot.” On the other hand, alight emitting particle having a particle size in a range in which theemission wavelength does not substantially depend on the particle sizeis referred to as a “non-quantum dot.”

Note that the particle size at which the quantum size effect isexhibited varies depending on the parameters of μ and ε, but when μ=0.1and ε=10 are assumed as typical semiconductors, approximately r=3r_(B)is a boundary of the particle size (radius) at which the quantum sizeeffect is exhibited. In FIG. 2 , the boundary is indicated by a brokenline.

As described above, the particle size at which the quantum size effectis exhibited in the light emitting particles is basically characterizedin relation to the exciton Bohr radius r_(B), but the dielectricconstant of the substance and the effective mass of electron holes arealso involved in the expression of the quantum size effect, and thechange in the value of E_(ex) is also continuous. Therefore, it isactually difficult to uniquely express the boundary between the quantumdot and the non-quantum dot by the particle size and other physicalproperty values.

FIG. 3 is a graph showing the particle radius dependency of E_(ex)calculated using typical physical property values (m_(e)*=0.3 m₀,m_(h)*=0.5 m₀, ε=6ε₀, E_(g,bulk)=1.93 eV) of BaZrS₃ as a representativechalcogenide perovskite material. m₀ is the mass of electrons. Thevertical axis of FIG. 3 represents the lowest excitation energy (eV),and the horizontal axis of FIG. 3 represents the particle radius (nm).

In the example of BaZrS₃ shown in FIG. 3 , the effective particle radiusof a typical quantum size is considered to be approximately 7.5 nm.Therefore, in the example of BaZrS₃, particles having a particle size of15 nm or less are considered as quantum dots, and particles having aparticle size of more than 15 nm are considered as non-quantum dots.

The core 11 of the present embodiment may be either the quantum dot orthe non-quantum dot.

When the core 11 is a quantum dot, there is an advantage that theemission wavelength (color) can be controlled by changing the particlesize of the same substance. In the case of the quantum dot, the lightemission efficiency of the core 11 is high, and the peak is narrow.

However, in order to align emission wavelengths (colors), strictparticle size control is required, and an advanced producing techniqueis required for producing quantum dots. In addition, the quantum dotshave poor chemical stability because of the fine particles thereof, andare easily aggregated, regrown, or decomposed, and thus require surfaceprotection. In addition, since the quantum dots have discrete electronicstates, the state density is small in both the valence band and theconduction band, and the light absorption coefficient is smaller thanthat of the bulk.

On the other hand, when the core 11 is a non-quantum dot, that is, whenbulk light emission is used without expressing a quantum size effectusing relatively large particles, problems of stability and lightabsorption are reduced. However, in the non-quantum dot, since theemission wavelength of the core 11 is determined by E_(g,bulk), it isnecessary to change E_(g,bulk) by changing the composition and thecrystal structure in order to adjust the emission wavelength.

As described above, since both the quantum dot and the non-quantum dothave advantages and disadvantages, as the configuration of the core 11,an appropriate configuration may be selected from the quantum dot andthe non-quantum dot according to the situation and application. Inaddition, since the dimension in which the quantum size effect occursvaries depending on the material, the particle size of the core 11 isappropriately set according to the physical properties of the material,and the like.

On the other hand, in order to suppress the reabsorption by the core 11,the particle size of the core 11 is preferably small. The opticalcoefficient of BaZrS₃ disclosed in Literature “Y. Nishigaki et al., Sol.RRL 1900555 (2020).” is used to calculate the ratio of light reabsorbedby the core 11. For example, when the particle size of BaZrS₃ is 200 nm,10% of red light having a wavelength of 630 nm generated in the core ofanother BaZrS₃ disposed in the vicinity is absorbed. Therefore, theparticle size of the core 11 is preferably 200 nm or less.

When the particle size of the core 11 is 50 nm or less under the aboveconditions, the reabsorption of red light having a wavelength of 630 nmis 3%, and when the particle size of the core 11 is 25 nm or less, thereabsorption of red light having a wavelength of 630 nm can besuppressed to 2% or less. Therefore, the particle size of the core 11 ispreferably 50 nm or less, and more preferably 25 nm or less.

The size of the particle size at which the core 11 can be stably presentis preferably 1 nm or more.

From the above, the particle size of the core 11 is preferably 1 nm ormore and 200 nm or less.

<Shell 12>

(Material of Shell)

The shell 12 is composed of a semiconductor material that absorbs atarget excitation light wavelength and generates excitation carriers.

As a material of the shell 12, for example, a group II-VI semiconductor,a group III-V semiconductor, a group I-III-VI semiconductor, a groupI-II-IV-VI semiconductor, a group IV-VI semiconductor, a halideperovskite semiconductor, an oxide perovskite, an organic-inorganicperovskite, Si, a carbon material, or a mixed crystal compound thereofcan be used.

In the color conversion particle, light emitted at the core orcore-shell interface passes through the shell and is extracted to theoutside. Therefore, the shell needs to transmit emitted light. Whenabsorption of light emitted in the shell occurs, the light emissionefficiency in the color conversion particle is reduced by that amount.Therefore, the band gap of the shell is preferably equal to or greaterthan the energy of emitted light.

In addition, chalcogenide perovskite can also be used as a material ofthe shell 12. By using the chalcogenide perovskite having an excellentlight absorption coefficient, the absorbance of the shell 12 can beincreased. In addition, in the chalcogenide perovskite shell 12, defectsat the interface between the core 11 and the shell 12 are reduced andnon-emissive recombination is reduced from the viewpoint of affinitywith constituent elements of the core and matching between the crystalstructure and the lattice constant, and thus higher light emissionefficiency of the core 11 can be expected.

As an example, when the chalcogenide perovskite is applied to thematerial of the shell 12, a material different from the material of thecore 11 can be selected from the following substances.

SrZrS₃, SrZrSe₃, SrHfS₃, SrHfSe₃, BaZrS₃, BaZrSe₃, BaHfS₃, BaHfSe₃,Sr₂Ba_(n−1)Zr_(n)S_(3n+1), Sr₂Ba_(n−1)Zr_(n)Se_(3n+1),Sr_(n+1)Zr_(n)S_(3n+1), Sr_(n+1)Zr_(n)Se_(3n+1),Ba₂Sr_(n−1)Zr_(n)S_(3n+1), Ba₂Sr_(n−1)Zr_(n)Se_(3n+1),Ba_(n+1)Zr_(n)S_(3n+1), Ba_(n+1)Zr_(n)Se_(3n+1),Sr₂Ba_(n−1)Hf_(n)S_(3n+1), Sr₂Ba_(n−1)Hf_(n)Se_(3n+1),Sr_(n+1)Hf_(n)S_(3n+1), Sr_(n+1)Hf_(n)Se_(3n+1),Ba₂Sr_(n−1)Hf_(n)S_(3n+1), Ba₂Sr_(n−1)Hf_(n)Se_(3n+1),Ba_(n+1)Hf_(n)S_(3n+1), and Ba_(n+1)Hf_(n)Se_(3n+1)

Similar to the case of the core 11, the chalcogenide perovskite that canbe applied to the shell 12 can also be expressed as(Sr_(x)Ba_(1−x))(Zr_(y)Hf_(1−y))(S_(z)Se_(1−z))₃ or(Sr_(x′)Ba_(1−x′))₂(Sr_(x)Ba_(1−x))_(n−1)(Zr_(y)Hf_(1−y))_(n)(S_(z)Se_(1−z))_(3n+1)(where each of x, x′, y, and z is a value from 0 to 1).

These substances are materials which are superior in having a band gapsuitable for applications that emit visible light, such as a lightemitting device, a display device, and a lighting device, when appliedto the shell 12 of the color conversion particle 10.

(Thickness of Shell)

The lower limit and the upper limit of the thickness of the shell 12 aredefined from the following viewpoints.

First, the shell 12 as the light absorption unit is required to have athickness capable of sufficiently absorbing the excitation light.

As an application of the color conversion particle 10, it is usuallyassumed that a large number of color conversion particles 10 arecontained in a film, a coating film, a resin, or the like and used as acolor conversion material. In this case, the shell 12 preferably has athickness having an excitation light absorption rate of at least 0.1% ormore. In addition, when the individual shells 12 have a thickness of atleast 2 nm, sufficient absorbance can be realized in the entire colorconversion material to which a large number of color conversionparticles are applied.

Second, when the thickness of the shell 12 is extremely thick, thephotoexcited carriers recombine and are deactivated before reaching thecore 11, and the light emission efficiency is reduced.

The diffusion length of photoexcited carriers or excitons variesdepending on the material, but is approximately several tens of nm toseveral hundreds of nm except in the case of an extremely high-qualitysingle crystal.

In addition, when the particle size of the color conversion particles 10is extremely large, when a large number of the color conversionparticles 10 are contained in a film, a coating film, a resin, or thelike, the gap between the particles increases, and the density of thecolor conversion particles 10 decreases. In the above case, as a result,the absorbance of the wavelength conversion material using the colorconversion particles 10 decreases.

Furthermore, when an ink in which the color conversion particles 10 aredispersed in a solvent is applied by, for example, an inkjet method,when the particle size of the color conversion particles 10 is extremelylarge, clogging of the nozzle occurs. In other coating methods, thelarge particle size of the color conversion particles 10 may be aproblem in the process.

For the above reason, the particle size of the color conversion particle10 is preferably 1000 nm or less. At this time, the thickness of theshell 12 as the light absorption unit is preferably 500 nm or less.

From the viewpoint of suppressing recombination of photoexcitedcarriers, as long as the shell 12 can sufficiently absorb excitationlight, the thickness of the shell 12 is preferably thinner, and forexample, the thickness of the shell 12 is preferably 50 nm or less, morepreferably 30 nm or less, and further more preferably 10 nm or less.

<Band Alignment of Core 11 and Shell 12>

As described above, in the core 11 and the shell 12, the band alignmentof energy E_(c) at the lower end of the conduction band and energy E_(v)at the upper end of the valence band induces the Stokes shift.

The Stokes shift originally indicates that there is an energy differencebetween an energy state of a photoexcited electron and an electronicstate when emitting energy and emitting light in a single substance, andis observed as a difference between maximum energy positions of anabsorption spectrum and an emission spectrum.

In a nanoparticle having a heterostructure such as the color conversionparticle 10 of the present embodiment, an “apparent Stokes shift,” thatis, an energy difference between an absorption spectrum end and anemission spectrum peak can be caused by designing an appropriate bandalignment at a heterointerface. In the present specification, theapparent Stokes shift that occurs in the heterostructure nanoparticlemay be referred simply to as the Stokes shift.

FIGS. 4, 5, and 6 illustrate examples of the band alignment of the core11 and the shell 12.

In each of FIGS. 4, 5, and 6 , the upper side indicates the direction inwhich the energy increases, the central rectangle indicates a band gapE_(g_core) of the core 11, and the rectangles on both sides indicate theband gap E_(g_shell) of the shell 12. The upper side of the centralrectangle indicates the energy E_(c_core) at the lower end of theconduction band of the core 11, and the bottom side of the centralrectangle indicates the energy E_(v_core) at the upper end of thevalence band of the core 11. The upper sides of the rectangles on bothsides indicate the energy E_(c_shell) at the lower end of the conductionband of the shell 12, and the bottom sides of the rectangles on bothsides indicate the energy E_(v_shell) at the upper end of the valenceband of the shell 12.

In each of FIGS. 4, 5, and 6 , a curve drawn on the upper side of therectangle indicates the distribution of electrons, and a curve drawn onthe bottom side of the rectangle indicates the distribution of holes. Inaddition, a downward arrow in the drawing indicates an energy differencein a light emission process, and an upward arrow in the drawingindicates an energy difference in a light absorption (excitation)process. The Stokes shift is induced when the energy difference in thelight absorption process is greater than the energy difference in thelight emission process.

In FIGS. 4(a) to 4(e), all of the band gaps E_(g_shell) of the shell 12are greater than the band gap E_(g_core) of the core 11(E_(g_shell)>E_(g_core)). On the other hand, in FIGS. 5(a) to 5(e), allof the band gaps E_(g_shell) of the shell 12 are less than the band gapE_(g_core) of the core 11 (E_(g_shell)<E_(g_core)). In addition, inFIGS. 6(a) to 6(c), all of the band gaps E_(g_shell) of the shell 12 areequal to the band gap E_(g_core) of the core 11(E_(g_shell)=E_(g_core)). Note that the magnitude relationship betweenE_(c_core) and E_(c_shell) and the magnitude relationship betweenE_(v_core) and E_(v_shell) are shown in each of FIGS. 4, 5, and 6 .

The Stokes shift is induced in the band alignment (Type I, Quasi-TypeII, and Type II) shown in FIGS. 4(a) to 4(e), 5(a), 5(e), 6(a), and6(c). Therefore, the color conversion particle of the present embodimenthas the band alignment of any of FIGS. 4(a) to 4(e), 5(a), 5(e), 6(a),and 6(c). The band alignment of the color conversion particles of thepresent embodiment satisfies at least one of a condition that the energyE_(c_shell) at the lower end of the conduction band of the shell 12 ishigher than the energy E_(c_core) at the lower end of the conductionband of the core 11, and the energy E_(v_shell) at the upper end of thevalence band of the shell 12 is lower than the energy E_(v_core) at theupper end of the valence band of the core 11 (that is, any one ofE_(c_shell)>E_(c_core), E_(v_shell)<E_(v_core), orE_(c_shell)>E_(c_core) and E_(v_shell)<E_(v_core))

The band alignments (Type I and Quasi-Type II) of FIGS. 4(b), 4(c), and4(d) satisfy all the conditions that the energy E_(c_shell) at the lowerend of the conduction band of the shell 12 is equal to or greater thanthe energy E_(c_core) at the lower end of the conduction band of thecore 11, and the energy E_(v_shell) at the upper end of the valence bandof the shell 12 is equal to or less than the energy E_(v_core) at theupper end of the valence band of the core 11 (that is, whenE_(g_shell)>E_(g_core), E_(c_shell)≥E_(c_core) andE_(v_shell)≤E_(v_core)).

In the case of Type I represented in FIG. 4(c), electrons and holes areconfined in the core 11, and recombination (core emission) occurs in thecore 11. In Type I, since holes and electrons are localized in the core11, the overlap of wave functions is large and the light emissionefficiency is high. Therefore, the configuration of Type I is the mostpreferable as the band alignment of the core 11 and the shell 12.Examples of the material of the core 11 and the shell 12 of Type Irepresented in FIG. 4(c) include a combination of BaZrS₃ as the core 11and SrZrS₃ as the shell 12.

In Quasi-Type II (where E_(g_shell)>E_(g_core)) represented by FIGS.4(b) and 4(d), carriers of one of holes or electrons spread in theshell, and thus the light emission efficiency is lower than that of TypeI. However, in FIGS. 4(b) and 4(d), since the other carrier is stilllocalized in the core, the light emission efficiency is relatively high,which is the second most preferable after Type I. Examples of thematerial of the core 11 and the shell 12 of Quasi-Type II represented inFIGS. 4(b) and 4(d) include a combination of BaHfS₃ as the core 11 andCaZrS₃ as the shell 12, which is shown in FIG. 4(b).

In addition, in the band alignment (Type II) of FIGS. 4(a), 4(e), 5(a),5(e), 6(a), and 6(c), electrons and holes are separated into the core 11and the shell 12, and thus light emission due to interband recombinationis less likely to occur as compared with Type I. However, in Type II,there is a possibility of recombination (interfacial emission) at theinterface between the core 11 and the shell 12, the energy difference issmaller than E_(g) of the shell 12, and thus the Stokes shift isinduced.

In the case of Type II, since light is emitted at the interface betweenthe core 11 and the shell 12, the overlap of wave functions is small,and the light emission efficiency is lower than that of Type I. Inaddition, interface recombination may be accompanied by non-emissiverecombination via interface defects, and thus it is considered thatlight emission efficiency is lowered also in this respect.

However, Type II is advantageous in that a wide range of emissionwavelengths can be realized even in the band alignment of Type II, andapplication to a near-infrared light emitting material or the like isexpected. Examples of the material of the core 11 and the shell 12 ofType II represented in FIGS. 4(a), 4(e), 5(a), 5(e), 6(a), and 6(c)include a combination of BaZrS₃ as the core 11 and CaZrS₃ as the shell12, which is shown in FIG. 4(a).

In addition, as shown in FIGS. 4(a) to 4(e), when the band gapE_(g_shell) of the shell 12 is made greater than the band gap E_(g_core)of the core 11 (E_(g_shell)>E_(g_core)), light emitted from the core 11is hardly absorbed by the shell 12 and is emitted to the outside. As aresult, the reabsorption loss in the shell 12 is suppressed, and thelight emission efficiency of the color conversion particle 10 can befurther improved.

In FIGS. 6(a) and 6(c), the band gaps E_(g_shell) of the shell 12 areequal to the band gap E_(g_core) of the core 11(E_(g_shell)=E_(g_core)). Therefore, in the cases of FIGS. 6(a) and6(c), light emitted from the core 11 is more likely to be reabsorbed bythe shell 12 than in the cases of FIGS. 4(a) to 4(e)(E_(g_shell)>E_(g_core)), and the reabsorption loss increases. For thisreason, the light emission efficiency of the color conversion particle10 decreases. In addition, when comparing the case where the band gapE_(g_shell) of the shell 12 is less than the band gap E_(g_core) of thecore 11 (E_(g_shell)<E_(g_core)) as shown in FIGS. 5(a) and 5(e) withthe cases of FIGS. 6(a) and 6(c), in the cases of FIGS. 6(a) and 6(c),the amount of light reabsorbed by the shell 12 is small and thereabsorption loss is suppressed, and thus the light emission efficiencyof the color conversion particles 10 can be improved.

Note that the color conversion particles 10 can take various statesdepending on the combination of the material of the core 11 and thematerial of the shell 12. The material of the core 11 and the materialof the shell 12 exemplified above are sulfides, but may be selenide or asolid solution, and when these are also included, various states can berealized, and there is a combination of the materials of the core 11 andthe shell 12 exhibiting excellent light emission characteristics.

<Method for Producing Color Conversion Particle 10>

Next, a method for producing the color conversion particle 10 will bedescribed. The color conversion particle 10 is produced by performing asynthesis step of the shell 12 after the synthesis step of the core 11.

(Synthesis Step of Core 11)

In the synthesis step of the core 11, the core 11, which is a nano-lightemitting particle, is formed of a chalcogenide perovskite. In this step,the core 11 may be synthesized by making the precursor compound react ina solution, the core 11 may be synthesized by mixing and heating theprecursor powder in an inert atmosphere or the atmosphere, or the core11 may be synthesized by mixing and heating the metal precursor powderin an inert atmosphere and making the mixture react with the chalcogenprecursor gas.

When the core 11 is synthesized by making the precursor compound reactin a solution, for example, a hot injection method, a heat-up method, asolvothermal method, a hydrothermal method, acomposite-hydroxide-mediated (CHM) method, a continuous flow processsynthesis method, or the like can be applied.

As an example, a case of synthesizing the core 11 of the chalcogenideperovskite ABX₃ in which A and B are made of Group II and Group IVelements, respectively, by applying a hot injection method will bedescribed.

In this case, a first solution containing a precursor compoundcontaining Group II elements, a precursor compound containing Group IVelements, and a solvent, and a second solution containing a precursorcompound containing chalcogen elements and a solvent are prepared. Then,the second solution is added to the first solution at a temperature inthe range of 130° C. to 400° C. in a reaction vessel, and the mixture isheld at the above-described temperature for 1 second to 100 hours in thereaction vessel to react. As a result, the core 11 of the targetchalcogenide perovskite compound is synthesized. After completion of thereaction, the reaction product is washed with an organic solvent orwater, and then the target product is collected.

Examples of the precursor compound containing Group II elementsdescribed above include the following compounds.

Metal powders, metal alkoxides, metal carboxylates, metal nitrates,metal perchlorates, metal sulfates, metal acetylacetonates, metalhalides, metal hydroxides, metal halides, and combinations thereof.

Examples of the precursor compound containing Group IV elementsdescribed above include the following compounds.

Metal powders, metal alkoxides, metal carboxylates, metal nitrates,metal perchlorates, metal sulfates, metal acetylacetonates, metalhalides, metal hydroxides, metal halides, and combinations thereof.

Examples of the precursor compound containing chalcogen elementsdescribed above include the following compounds.

Metal sulfide (including selenium substitute or tellurium substitute);

-   -   carbon disulfide (including selenium substitute or tellurium        substitute);    -   hydrogen chalcogenide such as hydrogen sulfide, hydrogen        selenide, and hydrogen telluride;    -   thiol compound (including selenium substitute or tellurium        substitute);    -   phosphine compound such as trioctylphosphine sulfide (including        selenium substitute or tellurium substitute); thiourea        (including selenium substitute or tellurium substitute); and    -   sulfur, selenium, tellurium, or    -   dispersions of these compounds in solvents such as amines,        acids, and hydrocarbons, and combinations thereof.

Examples of the solvent include the following solvents.

Primary amine, secondary amine, and tertiary amine having an organicgroup such as a hydrocarbon group;

-   -   aromatic hydrocarbon;    -   nitrogen-containing heterocyclic compound, oxygen-containing        heterocyclic compound, sulfur-containing heterocyclic compound,        selenium-containing heterocyclic compound, and tellurium        containing heterocyclic compound;    -   aliphatic hydrocarbon;    -   phosphine compound having an organic group such as a hydrocarbon        group;    -   phosphine oxide compound having an organic group such as a        hydrocarbon group; and    -   a commonly used organic solvent containing at least one of an        alcohol, an aldehyde, a carboxylic acid or a compound thereof        containing a sulfur-substituted group, a selenium-substituted        group, a tellurium-substituted group, or water, or, a        combination of these solvents

The heating of the solution includes making a precursor of the chalcogenelement react to form hydrogen chalcogenide. The reaction of the abovesolution includes synthesis under an inert atmosphere. Further, thereaction of the above solution may synthesize a target product in acontinuous flow process using a microreaction vessel.

In addition, as an example, a case where the chalcogenide perovskitecore 11 is synthesized by applying a heat-up method will be described.

In this case, a solution containing a precursor compound containingGroup II elements, a precursor compound containing Group IV elements, aprecursor compound containing chalcogen elements, and a solvent areprepared. Then, the above solution is heated from a room temperaturestate to a temperature in the range of 130° C. to 400° C. in a reactionvessel, and is held at the above-described temperature for 0 hours to100 hours in the reaction vessel to react. As a result, the core 11 ofthe target chalcogenide perovskite compound is synthesized. Aftercompletion of the reaction, the reaction product is washed with anorganic solvent or water, and then the target product is collected.

The precursor compound containing Group II elements, the precursorcompound containing Group IV elements, the precursor compound containingthe chalcogen elements, and the solvent are the same as those in thecase of the hot injection method.

The heating of the solution includes making a precursor of the chalcogenelement react to form hydrogen chalcogenide. The reaction vessel mayalso be pressurized during heating (solvothermal, hydrothermal).Further, the reaction of the above solution may synthesize a targetproduct in a continuous flow process using a microreaction vessel.

In addition, as an example, a case where the chalcogenide perovskitecore 11 is synthesized by applying a CHM method will be described.

In this case, a precursor compound containing Group II elements, aprecursor compound containing Group IV elements, a precursor compoundcontaining chalcogen elements, and sodium hydroxide and potassiumhydroxide are heated from a room temperature state to a temperature in arange of 130° C. to 400° C. in a reaction vessel, and held at theabove-described temperature for 0 hours to 200 hours in the reactionvessel to react. As a result, the core 11 of the target chalcogenideperovskite compound is synthesized. After completion of the reaction,the reaction product is washed with an organic solvent or water, andthen the target product is collected.

The precursor compound containing Group II elements, the precursorcompound containing Group IV elements, and the precursor compoundcontaining the chalcogen elements are the same as those in the case ofthe hot injection method.

In the CHM method, no solvent may be used, or some water may be added.In the CHM method, a mixture of sodium hydroxide and potassium hydroxideat a ratio of 51.5:48.5 is dissolved at 165° C. serves as a solvent. Thereaction vessel may also be pressurized during heating. Further, thereaction of the above solution may synthesize a target product in acontinuous flow process using a microreaction vessel.

In addition, as an example, a case where the chalcogenide perovskitecore 11 is synthesized by applying a solid phase synthesis method willbe described.

In this case, similar to the conventional solid phase synthesis method,a precursor compound containing Group II elements, a precursor compoundcontaining Group IV elements, and a precursor compound containingchalcogen elements are heated from a room temperature state to atemperature in a range of 400° C. to 1300° C. in a reaction vessel, andheld at the above-described temperature for 0 hours to 200 hours in thereaction vessel to react. As a result, the core 11 of the targetchalcogenide perovskite compound is synthesized.

The precursor compound containing Group II elements, the precursorcompound containing Group IV elements, and the precursor compoundcontaining the chalcogen elements are the same as those in the case ofthe hot injection method. The above synthesis also includes synthesisunder an inert atmosphere or an air atmosphere.

(Synthesis Step of Shell 12)

In the synthesis step of the shell 12, the shell 12 is synthesized onthe surface of the core 11 obtained in the above step. For example, thecolor conversion particles 10 having a core-shell structure may besynthesized by depositing a shell material on the surface of the core 11by a vapor phase growth method such as an ALD method or a CVD method. Asa method of synthesizing a shell, the shell 12 may be generated by, forexample, gas phase synthesis by barrel sputtering.

In the synthesis of the shell 12, a one-pot synthesis method or a hotinjection method may be applied. In this case, the nano-light emittingparticles to be the core 11 and the precursor of the shell material aremixed in a solvent. As a result, the color conversion particle 10 havinga core-shell structure in which the surface of the core 11 is coveredwith the shell material is synthesized. The one-pot synthesis method andthe hot injection method can also be applied to the case of forming theshell 12 of chalcogenide perovskite.

<External Structure of Color Conversion Particle 10>

As shown in FIG. 1(b), the color conversion particle 10 may have anouter shell 13 or a ligand 14 as a protective layer as an externalstructure.

(Outer Shell 13)

The outer shell 13 is a protective layer that covers the semiconductorparticles including the core 11 and the shell 12 from the outside. Theouter shell 13 is provided to further improve durability of the colorconversion particles 10 by suppressing deterioration of thesemiconductor particles due to oxygen contact and protecting thesemiconductor particles from chemical interaction with the outside. Theouter shell 13 has a property of transmitting target excitation lightand light emission of the core 11.

The outer shell 13 is formed by a known method using a chemically stablesubstance such as silica, glass, an oxide insulator, or a resin.

For example, when the outer shell 13 is formed of a metal oxide, siliconoxide, zirconium oxide, titanium oxide, aluminum oxide, or the like canbe used as a material. The outer shell 13 containing the metal oxide canbe formed by, for example, a method of forming an inorganic oxide by athermosetting reaction using a sol-gel method.

The outer shell 13 may be a layer containing a resin, a polysilazanemodified product, or the like. Polysilazane is a polymer having asilicon-nitrogen bond, and is a ceramic precursor inorganic polymercontaining SiO₂ composed of Si—N, Si—H, N—H and the like, Si₃N₄, anintermediate solid solution SiO_(x)N_(y) of both, and the like. When theouter shell 13 is formed of a resin, it is preferable that the outershell is formed of a water-soluble resin such as a polyvinylalcohol-based resin from the viewpoint of ease of production.

The outer shell 13 may have a multilayer structure including both ametal oxide layer and a layer containing a resin, a polysilazanemodified product, or the like.

(Ligand 14)

The ligand 14 is an organic modified molecule that surface-modifies thecolor conversion particle 10, and is bonded to the outer surface of thecolor conversion particle 10 or provided to cover the color conversionparticle 10.

The ligand 14 has a function of easily isolating the color conversionparticles 10 from each other to enhance dispersibility, and preventingregrowth, destruction, and the like due to contact between the colorconversion particles 10. In addition, the ligand 14 also has a functionof suppressing surface defects of the shell 12 by capping of thetangling bond and improving light emission efficiency.

As the modified organic molecule as the ligand 14, a modified organicmolecule having a structure having a nitrogen-containing functionalgroup, a sulfur-containing functional group, an acidic group, an amidegroup, a phosphine group, a phosphine oxide group, a hydroxyl group, alinear alkyl group, a carboxyl group, a phosphon group, a sulfone group,an amine group, or the like can be used. Examples of such a modifiedorganic molecule include sodium hexametaphosphate, sodium laurate,sodium dodecyl sulfate, sodium dodecylbenzene sulfonate, triethanolaminelauryl sulfate, lauryl diethanolamide, dodecyltrimethylammoniumchloride, trioctylphosphine, and trioctylphosphine oxide.

In addition, as the modified organic molecule as the ligand 14, it ispreferable to use a compound having a hydrophilic group and ahydrophobic group in the molecule. As a result, the color conversionparticle 10 can be covered with the ligand 14 in both a chemical bond inwhich a hetero atom is coordinate-bonded and a bond by physicaladsorption. Examples of this type of modified organic molecule includeamines which are compounds having a nonpolar hydrocarbon terminal as ahydrophobic group and an amino group as a hydrophilic group. When thehydrophilic group of the modified organic molecule is an amine, theamine can be firmly bonded to the metal element.

The modified organic molecule as the ligand 14 preferably has a heteroatom. When the modified organic molecule has a hetero atom, electricalpolarity between the hetero atom and the carbon atom occurs, and themodified organic molecule can be firmly bonded to the outer surface ofthe color conversion particle. Here, the “hetero atom” means all atomsexcept a hydrogen atom and a carbon atom.

<Modification Example of Color Conversion Particle>

Next, a modification example of the color conversion particle 10 will bedescribed with reference to FIGS. 7 and 8 . In the schematic diagrams ofthe color conversion particle 10 shown in FIGS. 7 and 8 , only the core11 and the shell 12 are shown unless otherwise specified. However, thesecolor conversion particles 10 may each have the outer shell 13 and theligand 14, similar to the example of FIG. 1(b).

For example, as shown in FIG. 7(a), the shell 12 of the color conversionparticle 10 does not necessarily cover the entire core 11, and a part ofthe core 11 may be exposed to the outside.

For example, as shown in FIG. 7(b), the color conversion particle 10 mayhave a structure in which a plurality of shells 12 are laminated andcovered outside one core 11. By using different materials such as acomposition and a crystal structure as the material of each shell 12,the light absorption characteristics and the light emissioncharacteristics of the entire color conversion particles 10 can beadjusted. In the example of FIG. 7(b), an example in which the two-layershells 12 a and 12 b are laminated on the core 11 is shown, but theshell 12 of the color conversion particle 10 may have three or morelayers.

The color conversion particle 10 having the multilayered shells 12 a and12 b shown in FIG. 7(b) can be formed by heating a solution containing asemiconductor particle in which the shell 12 a is formed on the core 11and another shell precursor.

For example, the color conversion particle 10 may have a structure inwhich the plurality of cores 11 are included in the shell 12 as shown inFIG. 7(c). When the plurality of cores 11 are included in the shell 12,the thickness of the effective shell 12 in the color conversionparticles 10 can increase and the durability of the color conversionparticles 10 can be improved. In addition, using different materialssuch as a composition and a crystal structure in each of the cores 11,the light absorption characteristics and the light emissioncharacteristics of the entire color conversion particles 10 can beadjusted.

In the example of FIG. 7(c), a structure in which three cores 11 areincluded in the shell 12 is shown, but the number of cores 11 includedin the shell 12 can be appropriately changed. In the color conversionparticle 10 having the plurality of cores 11, any of the cores 11 may bepartially exposed to the outside of the shell 12.

In addition, the color conversion particle 10 may have a structureincluding a plurality of cores 11 in the shell 12 and the shell 12having a plurality of layers. For example, as shown in FIG. 7(d), theouter side of the shell 12 a including the plurality of cores 11 mayfurther be covered with the shell 12 b. In addition, the shell mayfurther be laminated on the outer side of the shell 12 b in FIG. 7(d).

For example, as shown in FIG. 7(e), the plurality of cores 11 eachcovered with the shell 12 a may be covered with the shell 12 b andintegrated to form the color conversion particle 10. In the example ofFIG. 7(e), each of the shells 12 a may include the plurality of cores11.

The core 11 of the color conversion particle 10 may contain a lightabsorbing material 17 made of the same type of material as the shell 12.For example, as shown in FIG. 7(f), the outer side of the lightabsorbing material 17 may be covered with the core 11. Note that thematerial of the light absorbing material 17 may be, for example, amaterial that can be selected as the material of the shell 12, and theshell 12 covering the core 11 and the light absorbing material 17 maynot be made of the same material.

In the structure of the laminated core having the light absorbingmaterial 17 inside as described above, the excitation light transmittedthrough the outer shell 12 is absorbed by the light absorbing material17 (the same type of material of the shell 12) inside the core 11, andthe excitation light absorption rate can be improved. In addition, inthe structure of the laminated core having the light absorbing material17 therein, the photoexcited carriers are effectively confined in thenarrow region of the core 11 sandwiched between the materials of theshell 12, and accordingly, the light emission efficiency can beimproved.

In addition, the band alignment of the light absorbing material 17 andthe core 11 is preferably Type I, and the band alignment of the core 11and the shell 12 is also preferably Type I. Examples thereof include acombination of SrZrS₃ as the light absorbing material 17 and BaZrS₃ asthe core 11, and further, a combination of SrZrS₃ as the shell 12.Another examples thereof include a combination of SrHfS₃ as the lightabsorbing material 17 and BaHfS₃ as the core 11, and further, acombination of SrHfS₃ as the shell 12. Note that the band alignment ofthe light absorbing material 17 and the core 11 may be a combination ofmaterials whose the band alignment induces the Stokes shift, and thelight absorbing material 17 may be a material other than thechalcogenide perovskite.

Further, the color conversion particle 10 may have a hollow structurehaving a void 16 therein. For example, as shown in FIG. 8(a), one ormore voids 16 may be formed in the core 11. Alternatively, as shown inFIG. 8(b), in the color conversion particle 10 having the outer shell 13outside the shell 12, the void 16 may be formed between the shell 12 andthe outer shell 13. By forming the voids 16 that do not absorb or emitlight inside the color conversion particles 10, the opticalcharacteristics and shape of the color conversion particles 10 can beadjusted.

The color conversion particle 10 having a hollow structure shown inFIGS. 8(a) and 8(b) can be produced, for example, as follows. First, bysimultaneously adding an organic substance such as fullerene or carbonnanotube or a soluble salt at the time of synthesis, semiconductorparticles containing the organic substance or salt are generated.Thereafter, the organic substance or salt is dissolved using a solvent,or the organic substance or salt is ashed at a high temperature, andaccordingly the color conversion particles 10 having a hollow structurecan be obtained.

In addition, the core 11 or the shell 12 of the color conversionparticle 10 may contain a foreign substance that does not absorb andemit light, such as an insulator or other composition. By including theforeign substance in the core 11 or the shell 12, for example, the lightemission efficiency of the color conversion particle 10 can be improvedby scattering light, and the shape of the color conversion particle 10can be adjusted.

In addition, as shown in FIG. 8(c), the core 11 or the shell 12 of thecolor conversion particle 10 may have a gradient structure in whichphysical properties, such as composition, crystal structure, latticeconstant, density, crystal orientation, carrier concentration, band gap,defect density, dielectric constant, and conductivity, continuouslychange in a direction (depth direction) perpendicular to the interface.By continuously changing the physical properties or chemical propertiesof the core 11 or the shell 12 to form a gradient shape in the depthdirection, lattice matching can be enhanced, and lattice defects can bereduced. As a result, non-emissive recombination can be reduced, and thelight emission efficiency of the color conversion particles can beenhanced.

Note that the gradient structure described above can be produced by, forexample, the same method as in the case of producing the multilayer core11 or shell 12.

Furthermore, in the present invention, the shape of the color conversionparticle to be synthesized is not particularly limited. For example,spherical, elongated, star-shaped, polyhedral, pyramidal,tetrapod-shaped, tetrahedral, platelet, conical, irregularly shapedcores 11 and/or color conversion particles 10 can be synthesized.

Hereinafter, effects of the color conversion particle 10 of the presentembodiment will be described.

The color conversion particle 10 of the present embodiment includes thecore 11 and the shell 12 that contains the core 11 and absorbsexcitation light, and emits light at the core 11 or at the interfacebetween the core 11 and the shell 12 upon receiving the irradiatedexcitation light. The chalcogenide perovskite which is a material of thecore 11 has a high light absorption coefficient and excellentdurability. In addition, the core 11 and the shell 12 have bandalignment that induces the Stokes shift. In the present embodiment, byutilizing the difference between the band end transition energy of theshell 12 and the band end transition energy of the core 11, thephotoexcited carriers are transported to the core 11 by the shell 12,and the photoexcited carriers confined in the core 11 are recombined andemitted.

In the present embodiment, the part responsible for absorption and thepart responsible for light emission are separated in the colorconversion particle 10 by forming the shell 12 outside the chalcogenideperovskite core 11. Accordingly, it is possible to take a large Stokesshift, and the absorbance can be gained by the shell 12 withoutenlarging the core 11. Therefore, it is possible to achieve highabsorbance and high light emission efficiency while suppressing lightemission reabsorption loss by the core 11.

In addition, since the color conversion particle 10 of the presentembodiment has high absorbance and light emission efficiency asdescribed above, a desired color conversion function can be realizedwith a smaller amount as compared with conventional quantum dots and thelike. In other words, for example, in a case where the color conversionparticle 10 of the present embodiment is applied to a color conversionlayer of a display device, a lighting device, or the like, it ispossible to reduce the thickness of the color conversion layer andimprove the yield. In the formation of the color conversion layer, theprobability of occurrence of a defect in the film formation processincreases by repeating the film formation process many times, and as aresult, the yield of the color conversion layer decreases. Conversely,when the color conversion layer can be thinned, the film formationprocess can be reduced, and thus the effective defect rate of the colorconversion layer can be reduced.

In addition, when the band gap of the shell 12 is made greater than theband gap of the core 11, the light emitted from the core 11 is hardlyabsorbed by the shell 12 and is emitted to the outside, and thus thereabsorption loss in the shell can also be suppressed. That is, when theband gap of the shell 12 is greater than the band gap of the core 11,absorbance can be gained by thickening the shell 12 without increasingreabsorption loss, and thus the light emission efficiency in the colorconversion particles 10 can be further improved.

Furthermore, when the shell 12 is a chalcogenide perovskite, theabsorbance and durability of the shell 12 can be increased, and thelight emission efficiency can be further improved by reducing defects atthe core-shell interface.

<Product Form and Application Example of Color Conversion Particle 10>

Next, a product form and an application example of the color conversionparticle 10 will be described. Examples of the product form of the colorconversion particle 10 include a powder, a solution, a thin film, and asheet. As an application example of the color conversion particle 10,application to various devices is assumed.

(Powder)

The powder is in a state where the color conversion particles 10 areaggregated. Hereinafter, the color conversion particles 10 may bereferred to as primary particles, and those in which the colorconversion particles 10 are aggregated may be referred to as secondaryparticles. The sizes of the primary particles and the secondaryparticles are not particularly limited, but the primary particles arepreferably in the range of 5 nm to 1000 nm. In addition, a ligand may begiven to the surface of the primary particle or the secondary particle.In order to improve characteristics such as light emissioncharacteristics, dispersibility of the color conversion particles, andfilm formability, another material may be added to the powder of thecolor conversion particles 10 as an additive.

The application of the powder of the color conversion particles 10 isnot particularly limited. For example, a solution may be prepared bybeing dispersed in a solvent, a composite may be prepared by beingdispersed in a resin or a solid medium, a sputtering target may be usedas a sintered body, or a powder itself may be used as a source of avapor deposition source or the like.

Solution

The solution is in a state where the color conversion particles 10 aredispersed in a solvent. The sizes of the primary particles and thesecondary particles are not particularly limited, but the primaryparticles are preferably in the range of 5 nm to 1000 nm. The term“dispersed” refers to a state where the color conversion particles 10are floating or suspended in a solvent, and a part thereof may besettled. In addition, a ligand may be given to the surface of theprimary particle or the secondary particle.

As the solvent of the solution, one or more types of solvents may beused. Examples of the type of the solvent include those described below,and are not limited thereto. Water, esters such as methyl formate, ethylformate, propyl formate, pentyl formate, methyl acetate, ethyl acetate,and pentyl acetate; ketones such as γ-butyrolactone, acetone, dimethylketone, diisobutyl ketone, cyclopentanone, cyclohexanone, andmethylcyclohexanone; ethers such as diethyl ether, methyl-tert-butylether, diisopropyl ether, dimethoxymethane, dimethoxyethane,1,4-dioxane, 1,3-dioxolane, 4-methyldioxolane, tetrahydrofuran,methyltetrahydrofuran, anisole, and phenetol; alcohols such as methanol,ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, tert-butanol,1-pentanol, 2-methyl-2 butanol, methoxypropanol, diacetone alcohol,cyclohexanol, 2-fluoroethanol, 2,2,2-trifluoroethanol, and2,2,3,3-tetrafluoro-1 propanol; glycol ethers such as ethylene glycolmonomethyl ether, ethylene glycol monoethyl ether, ethylene glycolmonobutyl ether, ethylene glycol monoethyl ether acetate, andtriethylene glycol dimethyl ether; organic solvents having an amidegroup such as N-methyl-2 pyrrolidone, N,N-dimethylformamide, acetamide,and N,N-dimethylacetamide; organic solvents having a nitrile group, suchas acetonitrile, isobutyronitrile, propionitrile, ormethoxyacetonitrile; organic solvents having a carbonate group such asethylene carbonate or propylene carbonate; organic solvents havinghalogenated hydrocarbon group such as methylene chloride or chloroform;organic solvents having a hydrocarbon group such as n-pentane,cyclohexane, n-hexane, benzene, toluene, or xylene; and dimethylsulfoxide.

In addition, an acid, a base, a binder material, or the like may beadded to the above solution as an additive in order to improvecharacteristics such as light emission characteristics, dispersibilityof the color conversion particles 10, and film formability.

The application of the solution is not particularly limited. Forexample, the solution may be used for film formation by a coatingmethod, a spraying method, or a doctor blade method (other solution filmformation methods), preparation of a composite by compounding with asolid dispersion medium, or preparation of a device using them.

(Thin film)

The thin film is a state where the color conversion particles 10 areaggregated in a planar shape. The sizes of the primary particles and thesecondary particles are not particularly limited, but the primaryparticles are preferably in the range of 5 nm to 1000 nm. In addition, aligand may be given to the surface of the primary particle or thesecondary particle. In order to improve characteristics such as lightemission characteristics, and dispersibility of the color conversionparticles 10, another material may be added to the thin film describedabove as an additive.

The method for producing the thin film is not particularly limited. Forexample, the thin film may be prepared by producing a film using acoating method, a spraying method, a doctor blade method, an inkjetmethod, or other solution film formation methods, using a vacuum processsuch as a sputtering method or a vacuum vapor deposition method. Inaddition, the color conversion particles 10 may be formed into a film bycoating or other methods, and then the particle shape may not bemaintained by firing or other processing.

(Sheet)

The sheet is in a state where the dispersion medium in which the colorconversion particles 10 are dispersed is planar. The sizes of theprimary particles and the secondary particles are not particularlylimited, but the primary particles are preferably in the range of 5 nmto 1000 nm. In addition, a ligand may be given to the surface of theprimary particle or the secondary particle.

As the material used as the dispersion medium of the sheet, a polymerwell known to those skilled in the art that can be used for this type ofpurpose can be applied in any manner. In a suitable embodiment, polymersof this type are substantially translucent or substantially transparent.

For example, polymers applicable as a dispersion medium of a sheetinclude polyvinyl butyral, polyvinyl acetate, silicone, and derivativesof silicone, but are not limited thereto. In addition, derivatives ofsilicone include polyphenylmethylsiloxane, polyphenylalkylsiloxane,polydiphenylsiloxane, polydialkylsiloxane, fluorinated silicones andvinyl and hydride substituted silicones, ionomers, polyethylene,polyvinyl chloride, polyvinylidene chloride, polyvinyl alcohol,polypropylene, polyester, polycarbonate, polystyrene, polyacrylonitrile,ethylene vinyl acetate copolymer, ethylene-vinyl alcohol copolymer,ethylene-methacrylic acid copolymer film, nylon, and the like, but arenot limited thereto.

In order to improve characteristics such as light emissioncharacteristics and dispersibility of the color conversion particles 10,silica fine particles or other materials such as the solvent describedin the above solution may be added to the sheet described above as anadditive.

The method for producing the sheet is not particularly limited. Forexample, a sheet may be produced by kneading and stretching a powder anda dispersion medium, or a sheet may be produced by mixing and applyingan ink containing the color conversion particles 10 and a dispersionmedium or a precursor thereof.

(Device)

As an application of the color conversion particles 10, or the powder,solution, film, or sheet described above, application to down-conversionsuch as ultraviolet light or blue light in various devices is assumed.Examples of the type of device include a light emitting device such asan LED or an organic EL, a display device including the light emittingdevice, a lighting device including the light emitting device, an imagesensor, a photoelectric conversion device, a bioluminescent label, andthe like.

EXAMPLE

Hereinafter, an example of the color conversion particle of the presentinvention will be described.

In the color conversion particles of the example, the material of thecore is BaZrS₃, and the material of the shell is SrZrS₃. That is, in thecolor conversion particles of the example, the core and the shell arechalcogenide perovskites, and correspond to an example of a combinationof the best materials that induce the Stokes shift. As described above,when the core and the shell are chalcogenide perovskites, interfacedefects between the core and the shell are reduced, and high lightemission efficiency can be expected.

FIG. 9 is a diagram showing band alignment of shell/core/shell in thecolor conversion particles of the example. The origin of the energy onthe vertical axis is a vacuum level. The physical property values of thecore and the shell were determined in a comprehensive manner from otherexperimental result reports with reference to Literature “Y. Nishigakiet al., Sol. RRL 1900555 (2020).” and Literature “K. Hanzawa et al., J.Am. Chem. Soc. 141, 5343 (2019).”

As shown in FIG. 9 , since E_(c) of the core is lower than E_(c) of theshell and E_(v) of the core is higher than E_(v) of the shell, the bandalignment of the shell and the core in the example is Type I. Therefore,in the configuration of the example, it is expected that the excitationlight is absorbed by the shell, and the excited carriers move to thecore and recombine to emit the core light. In addition, in the example,since the band gap E_(g) of the shell is greater than the band gap E_(g)of the core, suppression of the reabsorption loss in the shell is alsoexpected.

In the example, one-dimensional simulations were conducted usingsoftware (SCAPS-1D) for the absorption and emission of the colorconversion particles. FIG. 10 is a diagram showing a result ofsimulation of the example. The horizontal axes in each drawing of FIG.10 respectively represent the one-dimensional position in the diameterdirection of the color conversion particle.

In the simulation, the diameter of the core was set to 20 nm, and thethickness of the shell was set to 50 nm. In addition, the wavelength ofthe excitation light was set to blue light of 450 nm, and the excitationlight was set to be incident from one side (left side in the drawing) atan illuminance of 100 mW/cm².

FIG. 10(a) shows a profile of E_(c) of the color conversion particle,and FIG. 10(b) shows a profile of E_(v) of the color conversionparticle. The energy on the vertical axis is based on the Fermi energyE_(F).

In FIG. 10(a), E_(c) in a core range (the range in which the value onthe horizontal axis is 50 nm to 70 nm) is lower than E_(c) in the shellrange. In FIG. 10(b), E_(v) in the core range is higher than E_(v) inthe shell range. The profiles in FIGS. 10(a) and 10(b) match well withthe band alignment shown in FIG. 9 .

FIG. 10(c) shows the carrier concentration distribution of the colorconversion particles. A solid line in FIG. 10(c) indicates a profile ofan electron, and a broken line in FIG. 10(c) indicates a profile of ahole.

In FIG. 10(c), the carrier density in the core range (the range in whichthe value on the horizontal axis is 50 nm to 70 nm) is higher than thatin the shell range. Therefore, it can be seen in FIG. 10(c) thatcarriers excited by light absorbed by the shell are effectively moved tothe core and confined.

FIG. 10(d) shows a generation rate and a recombination rate of carriers.The broken line in FIG. 10(d) indicates the profile of the generationrate of the carriers, and the solid line in FIG. 10(d) indicates theprofile of the recombination rate of the carriers.

As shown in FIG. 10(d), the generation rate of the carriers is thehighest on the left side in the drawing where the excitation light isincident. In addition, since the light absorption coefficient of thechalcogenide perovskite is extremely large, the generation rate of thecarriers rapidly decreases toward the right side in the drawing. It canbe seen that most of the carrier excitation by light absorption occursin the shell range of 0 nm to 50 nm.

On the other hand, the recombination rate of the carriers shows a highvalue over the core range (the range in which the value of thehorizontal axis is 50 nm to 70 nm), and the value is almost 0 in theshell range. That is, light emission due to carrier recombination ismostly caused by photoexcited carriers that have moved to the core.

Therefore, it can be seen from the result of simulation that transportof the photoexcited carriers from the shell to the core and confinementof the photoexcited carriers to the core effectively occur.

In addition, light absorption coefficients of BaZrS₃ and SrZrS₃ andphotoluminescence (PL) emission peaks of BaZrS₃ were respectivelycalculated based on the optical coefficients of BaZrS₃ and SrZrS₃indicated in the above “Y. Nishigaki et al., Sol. RRL 1900555 (2020).”

FIG. 11 is a diagram showing respective profiles of the light absorptioncoefficients of BaZrS₃ and SrZrS₃ and PL emission spectrum of BaZrS₃. InFIG. 11 , the horizontal axis represents the wavelength.

The PL emission spectrum (solid line in FIG. 11 ) of BaZrS₃, which is amaterial of the core, shows a sharp emission peak having a half-valuewidth of approximately 30 nm. This is because the absorption end (therise of the light absorption coefficient near the band end) of thechalcogenide perovskite is extremely steep.

In addition, an alternate long and short dash line in FIG. 11 indicatesthe profile of the light absorption coefficient of BaZrS₃, and a brokenline in FIG. 11 indicates the profile of the light absorptioncoefficient of SrZrS₃. In a region where the profile of the PL emissionspectrum overlaps with the tail part of the profile of the lightabsorption coefficient, the light emission can be reabsorbed.

That is, it can be seen that light emission can be reabsorbed when colorconversion is performed only with BaZrS₃ that is a material of the core.Therefore, in the case of the core of BaZrS₃, when the particle size isincreased in order to gain the absorbance, the reabsorption is alsoincreased, and thus the magnitude of the absorbance and the loss of thereabsorption are in a trade-off relationship.

On the other hand, the tail part of the profile of the light absorptioncoefficient of SrZrS₃ hardly overlaps with the profile of the PLemission spectrum of BaZrS₃. Therefore, it can be seen that when theshell of SrZrS₃ is applied to the core of BaZrS₃, reabsorption in theshell hardly occurs.

In the example, the color conversion particles have a core-shellstructure, and SrZrS₃, which is a shell material having a greater bandgap than BaZrS₃ of the core, gains the absorbance of the excitationlight. Therefore, in the configuration of the example, the thickness ofthe shell can be increased to gain the absorbance without increasing thereabsorption loss.

FIG. 12 is a diagram showing a correspondence between the combination ofmaterials of the core and the shell, and the type of the band alignmentand expression of the Stokes shift in the example and the comparativeexample. In FIG. 12 , the type of band alignment and the presence orabsence of expression of the Stokes shift are shown in association with16 combinations (4×4=16) in a case where four types of materials ofSrZrS₃, BaZrS₃, SrHfS₃, and BaHfS₃ are applied to the materials of thecore and the shell.

In FIG. 12 , a combination of materials in which the Stokes shift isinduced (Yes) is an example, and a combination of materials in which theStokes shift is not induced (No) is a comparative example. Here, in FIG.12 , in cases where the core and the shell are the same material, thetypes of band alignment are all Flat, and in these cases, the Stokesshift is not induced.

In FIG. 12 , when the material of the core is SrZrS₃ and the material ofthe shell is BaZrS₃, the type of the band alignment is Inverse Type I,and the Stokes shift is not induced in this combination. On the otherhand, when the material of the core is SrZrS₃ and the material of theshell is SrHfS₃ or BaHfS₃, the types of band alignments are all Type II,and the Stokes shift is induced in any of these combinations.

In FIG. 12 , when the material of the core is BaZrS₃ and the material ofthe shell is SrZrS₃, the type of the band alignment is Type I. Inaddition, in a case where the material of the core is BaZrS₃ and thematerial of the shell is SrHfS₃ or BaHfS₃, the types of band alignmentsare all Type II. Both of these combinations express the Stokes shift.

In FIG. 12 , when the material of the core is SrHfS₃ and the material ofthe shell is SrZrS₃ or BaZrS₃, the types of band alignments are all TypeII, and the Stokes shift is induced in any of these combinations. On theother hand, when the material of the core is SrHfS₃ and the material ofthe shell is BaHfS₃, the type of the band alignment is Inverse Type I,and the Stokes shift is not induced in this combination.

In FIG. 12 , in a case where the material of the core is BaHfS₃ and thematerial of the shell is SrZrS₃ or BaZrS₃, the types of band alignmentsare all Type II. In addition, when the material of the core is BaHfS₃and the material of the shell is SrHfS₃, the type of the band alignmentis Type I. Both of these combinations express the Stokes shift.

Note that, in both the case where the material of the core is BaZrS₃ andthe material of the shell is SrZrS₃ and the case where the material ofthe core is BaHfS₃ and the material of the shell is SrHfS₃, the type ofband alignment is Type I, and thus, it is possible to obtain colorconversion particles particularly excellent in light emissioncharacteristics.

As described above, the embodiment of the present invention has beendescribed, but the embodiment is presented as an example, and is notintended to limit the scope of the present invention. The embodimentscan be implemented in various forms other than the above, and variousomissions, substitutions, changes, and the like can be made withoutdeparting from the gist of the present invention. Embodiments andmodifications thereof are included in the scope and gist of the presentinvention, and the invention described in the claims and equivalentsthereof are also included in the scope and gist of the presentinvention.

The present application claims priority based on Japanese PatentApplication No. 2020-195173 filed on Nov. 25, 2020, and the entirecontents of Japanese Patent Application No. 2020-195173 are incorporatedherein by reference.

REFERENCE SIGNS LIST

-   -   10 Color conversion particle    -   11 Core    -   12, 12 a, 12 b Shell    -   13 Outer shell    -   14 Ligand    -   16 Void

1. A color conversion particle comprising: a core; and a shell thatcontains the core and absorbs excitation light, wherein light is emittedat the core or at an interface between the core and the shell uponreceiving the irradiated excitation light, the core is composed of achalcogenide perovskite, and the core and the shell have band alignmentthat induces a Stokes shift.
 2. The color conversion particle accordingto claim 1, wherein the chalcogenide perovskite has a crystal structureof any one of crystal structures of a cubic perovskite, a tetragonalperovskite, a GdFeO₃ type orthorhombic perovskite, a Ruddlesden-Poppertype layered perovskite, a Dion-Jacobson type layered perovskite, and adouble perovskite.
 3. The color conversion particle according to claim1, wherein the chalcogenide perovskite has a chemical formula of ABX₃ orA′₂A_(n−1)B_(n)X₃₁+(A and A′ are Group 2 elements, B is a Group 4element, X is a chalcogen element, and n is an integer of 1 or more). 4.The color conversion particle according to claim 3, wherein the A, theA′, the B, and the X include a mixture of elements of respective groupsat any ratio.
 5. The color conversion particle according to claim 1,wherein the chalcogenide perovskite is selected from any one of CaTiS₃,CaTiSe₃, CaTiTe₃, CaZrS₃, CaZrSe₃, CaZrTe₃, CaHfS₃, CaHfSe₃, CaHfTe₃,SrTiS₃, SrTiSe₃, SrTiTe₃, SrZrS₃, SrZrSe₃, SrZrTe₃, SrHfS₃, SrHfSe₃,SrHfTe₃, BaTiS₃, BaTiSe₃, BaTiTe₃, BaZrS₃, BaZrSe₃, BaZrTe3, BaHfS₃,BaHfSe₃, BaHfTe₃, Ca₂Ba_(n−1)Ti_(n)S_(3n+1), Ca₂Ba_(n−1)Ti_(n)Se_(3n+1),Ca₂Ba_(n−1)Ti_(n)Te_(3n+1), Ca₂Ba_(n−1)Zr_(n)S_(3n+1),Ca₂Ba_(n−1)Zr_(n)Se_(3n+1), Ca₂Ba_(n−1)Zr_(n)Te_(3n+1),Ca₂Ba_(n−1)Hf_(n)S_(3n+1), Ca₂Ba_(n−1)Hf_(n)Se_(3n+1),Ca₂Ba_(n−1)Hf_(n)Te_(3n+1), Ca₂Sr_(n−1)Ti_(n)S_(3n+1),Ca₂Sr_(n−1)Ti_(n)Se_(3n+1), Ca₂Sr_(n+1)Ti_(n)Te_(3n+1),Ca₂Sr_(n−1)Zr_(n)S_(3n+1), Ca₂Sr_(n−1)Zr_(n)Se_(3n+1),Ca₂Sr_(n−1)Zr_(n)Te_(3n+1), Ca₂Sr_(n−1)Hf_(n)S_(3n+1),Ca₂Sr_(n−1)Hf_(n)Se_(3n+1), Ca₂Sr_(n−1)Hf_(n)Te_(3n+1),Sr₂Ca_(n−1)Ti_(n)Se_(3n+1), Sr₂Ca_(n−1)Ti_(n)Se_(3n+1),Sr₂Ca_(n−1)Ti_(n)Te_(3n+1), Sr₂Ca_(n−1)Zr_(n)S_(3n+1),Sr₂Ca_(n−1)Zr_(n)Se_(3n+1), Sr₂Ca_(n−1)Zr_(n)Te_(3n+1),Sr₂Ca_(n−1)Hf_(n)S_(3n+1), Sr₂Ca_(n−1)Hf_(n)Se_(3n+1),Sr₂Ca_(n−1)Hf_(n)Te_(3n+1), Sr₂Ba_(n−1)Ti_(n)S_(3n+1),Sr₂Ba_(n−1)Ti_(n)Se_(3n+1), Sr₂Ba_(n−1)Ti_(n)Te_(3n+1),Sr₂Ba_(n−1)Zr_(n)S_(3n+1), Sr₂Ba_(n−1)Zr_(n)Se_(3n+1),Sr₂Ba_(n−1)Zr_(n)Te_(3n+1), Sr₂Ba_(n−1)Hf_(n)S_(3n+1),Sr₂Ba_(n−1)Hf_(n)Se_(3n+1), Sr₂Ba_(n−1)Hf_(n)Te_(3n+1),Ba₂Ca_(n−1)Ti_(n)S_(3n+1), Ba₂Ca_(n−1)Ti_(n)Se_(3n+1),Ba₂Ca_(n−1)Ti_(n)Te_(3n+1), Ba₂Ca_(n−1)Zr_(n)S_(3n+1),Ba₂Ca_(n+1)Zr_(n)Se_(3n+1), Ba₂Ca_(n−1)Zr_(n)Te_(3n+1),Ba₂Ca_(n−1)Hf_(n)S3_(n+1), Ba₂Ca_(n−1)Hf_(n)Se_(3n+1),Ba₂Ca_(n−1)Hf_(n)Te_(3n+1), Ba₂Sr_(n+1)Ti_(n)S_(3n+1),Ba₂Sr_(n+1)Ti_(n)Se_(3n+1), Ba₂Sr_(n+1)Ti_(n)Te_(3n+1),Ba₂Sr_(n−1)Zr_(n)S_(3n+1), Ba₂Sr_(n−1)Zr_(n)Se_(3n+1),Ba₂Sr_(n−1)Zr_(n)Te_(3n+1), Ba₂Sr_(n−1)Hf_(n)S_(3n+1),Ba₂Sr_(n−1)Hf_(n)Se_(3n+1), Ba₂Sr_(n−1)Hf_(n)Te_(3n+1),Ca_(n+1)Ti_(n)S_(3n+1), Ca_(n+1)Ti_(n)Se_(3n+1),Ca_(n+1)Ti_(n)Te_(3n+1), Ca_(n+1)Zr_(n)S_(3n+1),Ca_(n+1)Zr_(n)Se_(3n+1), Ca_(n+1)Zr_(n)Te_(3n+1),Ca_(n+1)Hf_(n)S_(3n+1), Ca_(n+1)Hf_(n)Se_(3n+1),Ca_(n+1)Hf_(n)Te_(3n+1), Sr_(n+1)Ti_(n)S_(3n+1),Sr_(n+1)Ti_(n)Se_(3n+1), Sr_(n+1)Ti_(n)Te_(3n+1),Sr_(n+1)Zr_(n)S3_(n+1), Sr_(n+1)Zr_(n)Se_(3n+1),Sr_(n+1)Zr_(n)Te_(3n+1), Sr_(n+1)Hf_(n)S_(3n+1),Sr_(n+1)Hf_(n)Se_(3n+1), Sr_(n+1)Hf_(n)Te_(3n+1),Ba_(n+1)Ti_(n)S_(3n+1), Ba_(n+1)Ti_(n)Se_(3n+1),Ba_(n+1)Ti_(n)Te_(3n+1), Ba_(n+1)Zr_(n)S_(3n+1),Ba_(n+1)Zr_(n)Se_(3n+1), Ba_(n+1)Zr_(n)Te_(3n+1),Ba_(n+1)Hf_(n)S_(3n+1), Ba_(n+1)Hf_(n)Se_(3n+1), andBa_(n+1)Hf_(n)Te₃n+1 (where n is an integer of 1 or more).
 6. The colorconversion particle according to claim 1, wherein the chalcogenideperovskite is(Ca_(x)Sr_(x′)Ba_(1−x−x′))(Ti_(y)Zr_(y′)Hf_(1−y−y′))(S_(z)Se_(z′)Te_(1−z−z′))₃or(Ca_(w)Sr_(w′)Ba_(1−w−w′))₂(Ca_(x)Sr_(x′)Ba_(1−x−x′))_(n−1)(Ti_(y)Zr_(y′)Hf_(1−y−y′))_(n)(S_(z)Se_(z′)Te_(1−z−z′))_(3n+1)(where each of w, w′, x, x′, y, y′, z and z′ is a value from 0 to 1;w+w′≤1, x+x′≤1, y+y′≤1, z+z′≤1).
 7. The color conversion particleaccording to claim 1, wherein the band alignment satisfies at least oneof a condition that energy E_(c_shell) at a lower end of a conductionband of the shell is higher than energy E_(c_core) at a lower end of aconduction band of the core and a condition that energy E_(v_shell) atan upper end of a valence band of the shell is lower than energyE_(v_core) core at an upper end of a valence band of the core.
 8. Thecolor conversion particle according to claim 7, wherein a band gap ofthe shell is greater than a band gap of the core.
 9. The colorconversion particle according to claim 8, wherein the band alignmentsatisfies a condition that energy E_(c_shell) at a lower end of aconduction band of the shell is higher than energy E_(c_core) at a lowerend of a conduction band of the core and energy E_(v_shell) at an upperend of a valence band of the shell is lower than energy E_(v_core) at anupper end of a valence band of the core.
 10. The color conversionparticle according to claim 1, wherein a particle size of the core is 1nm or more and 200 nm or less.
 11. The color conversion particleaccording to claim 10, wherein a particle size of the core is 1 nm ormore and 50 nm or less.
 12. The color conversion particle according toclaim 11, wherein a particle size of the core is 1 nm or more and 25 nmor less.
 13. The color conversion particle according to claim 1, whereinthe shell has a plurality of layers.
 14. The color conversion particleaccording to claim 1, wherein the shell has a plurality of the cores.15. The color conversion particle according to claim 1, wherein the corecontains a light absorbing material.
 16. The color conversion particleaccording to claim 1, wherein at least one of the shell or the coreincludes a foreign substance or a void.
 17. The color conversionparticle according to claim 1, wherein at least one of the shell and thecore has a structure in which physical properties change in a gradientmanner in a depth direction.
 18. The color conversion particle accordingto claim 1, wherein the shell is composed of a chalcogenide perovskitedifferent from the core.
 19. The color conversion particle according toclaim 18, wherein the chalcogenide perovskite different from the core isselected from any one of SrZrS₃, SrZrSe₃, SrHfS₃, SrHfSe₃, BaZrS₃,BaZrSe₃, BaHfS₃, BaHfSe₃, Sr₂Ba_(n−1)Zr_(n)S_(3n+1),Sr₂Ba_(n−1)Zr_(n)Se_(3n+1), Sr_(n+1)Zr_(n)S_(3n+1),Sr_(n+1)Zr_(n)Se_(3n+1), Ba₂Sr_(n−1)Zr_(n)S_(3n+1),Ba₂Sr_(n−1)Zr_(n)Se_(3n+1), Ba_(n+1)Zr_(n)S_(3n+1),Ba_(n+1)Zr_(n)Se_(3n+1), Sr₂Ba_(n−1)Hf_(n)S_(3n+1),Sr₂Ba_(n−1)Hf_(n)Se_(3n+1), Sr_(n+1)Hf_(n)S_(3n+1),Sr_(n+1)Hf_(n)Se_(3n+1), Ba₂Sr_(n−1)Hf_(n)S_(3n+1),Ba₂Sr_(n−1)Hf_(n)Se_(3n+1), Ba_(n+1)Hf_(n)S_(3n+1), andBa_(n+1)Hf_(n)Se_(3n+1) (where n is an integer of 1 or more).
 20. Thecolor conversion particle according to claim 18, wherein thechalcogenide perovskite different from the core is(Sr_(x)Ba_(1−x))(Zr_(y)Hf_(1−y))(S_(z)Se_(1−z))₃ or(Sr_(x)Ba_(1−x′))₂(Sr_(x)Ba_(1−x))_(n+1)(Zr_(y)Hf_(1−y))_(n)(S_(z)Se_(1−z))_(3n+1)(where each of x, x′, y, and z is a value from 0 to 1).
 21. The colorconversion particle according to claim 19, wherein the core is BaZrS₃,and the shell is SrZrS₃.
 22. The color conversion particle according toclaim 19, wherein the core is BaHfS₃, and the shell is SrHfS₃.
 23. Apowder comprising the color conversion particle according to a claim 1.24. A solution comprising the color conversion particle according toclaim
 1. 25. A thin film comprising the color conversion particleaccording to a claim
 1. 26. A sheet comprising the color conversionparticle according to claim
 1. 27. A device comprising the colorconversion particle according to claim 1.